Robotic arms have been employed for positioning components onto printed circuit boards. In the precise position of the components, potential misalignment problems between the leads of a fine pitch component, such as a large scale integrated circuit, and the pads of a substrate site, such as a printed circuit board, can develop. The misalignment can be caused by the handling of the component or device prior to placement onto the printed circuit board. Also, there can be non-coplanarity between the device leads and the substrate site during placement, and in this regard, if the leads contact the substrate site other than substantially simultaneously, translational forces will result either moving the robotic arm or the location of the substrate itself. Moreover, misalignment can also be caused by movement induced by the reflow process itself. Therefore, it would be highly desirable for any robotic system utilized in surface mount technology to reduce greatly, if not eliminate entirely, such unwanted misalignment between the leads of an integrated circuit device relative to the pads of a printed circuit board.
Prior known robotic systems utilized for the placement and assembly of fine pitch devices onto printed circuit board substrates have proven less than totally satisfactory. Such systems have not successfully reduced or substantially eliminated the non-coplanarity problems between the fine pitch leads of the device and the substrate surface.
One attempted solution at solving the aforementioned non-coplanarity problem, has been the heated bar reflow soldering method. In this regard, in order to solve the non-coplanarity problem, a plurality of heated bars are brought into direct contact with the leads of the electronic device to apply heat to the pads of a printed circuit board and also to apply direct force to the leads of the device simultaneously therewith, to maintain lead alignment with the pads of the printed circuit board during a reflow soldering operation. While this attempted solution has proven satisfactory with standard pitch devices, the coupling of the hot bar tool via a tool adaptor to a robotic control source has caused other problems.
For example, conventional large scale integrated devices are generally rectangular in shape with a large number of fine pitch leads extending from all four sides of the body of the device. This type of device configuration requires a hot bar tool with a set of hot bars in a generally rectangular configuration for engaging simultaneously all the leads of the device. Also, in order to control accurately the heating process for each hot bar, separate thermocouples must be attached to each respective hot bar for monitoring its temperature. Thus, any tool adaptor coupling the hot bar tool to a robotic control source must include a plurality of connectors for supplying high current to each respective hot bar, and for carrying thermocouple information to the robotic control source.
The necessity for having a large number of connectors produces two unwanted and undesirable problems. Firstly, greater frictional forces must be overcome to connect the tool to the robotic unit. In this regard, by increasing the number of connectors, a greater contact surface area is established between the robotic control source and the tool adaptor itself. This in turn, results in a substantially greater force being required to engage and disengage the tool adaptor from the robotic control source.
Secondly, a greater distance is required between the working surface of the robotic tool and the mounting surface of the robotic unit. In this regard, in order to accommodate the high current connectors for energizing the individual hot bars, either the height or the diameter of the tool adaptor, must be increased.
Implementing solutions to the above mentioned problems has proven difficult, if not entirely impossible. In this regard, because of the larger contact surface area, greater frictional forces must be overcome to engage the tool adaptor with the robotic control source. However, the pneumatic power available through most conventional robotic control sources is generally limited and thus, larger driving mechanisms cannot be easily incorporated into prior known tool changing devices for engagement/disengagement purposes. Moreover, even when sufficient pneumatic power is available, adding a larger driving mechanism merely compounds the second problem mentioned above; namely, that either the height or the diameter of the tool adaptor must be increased to accommodate the larger driving mechanism. However, increasing the height or diameter of the tool changing device introduces still yet other problems.
With respect to increasing the height of a tool changing device, a greater distance is established between the distal end of the hot bar tool and the robotic arm attachment surface. This greater distance tends to magnify any non-coplanarity problems between the leads of an electronic device held by the tool and the substrate site during placement with attendant lead to pad misalignment. On the other hand, increasing the diameter of a tool changing device results in an off center low profile construction that not only decreases the payload weight of the robotic tool changing system, but also causes unwanted and undesired deflection errors. In this regard, the off center construction coupled with the increased weight results in forces from the robotic control source to the tool changing device being shifted or distributed unequally, thus inducing undesired deflection errors.
Therefore it would be highly desirable to have a new and improved robotic tool adaptor and system and method for connecting and disconnecting a surface mount processing tool, such as a hot bar reflow soldering head to a robotic control source to overcome the problem associated with using either high profile tool adaptors or large diameter low profile tool adaptors. Such a tool adaptor and system and method of using them should greatly reduce, if not entirely eliminate misalignment of the leads of a fine pitch electronic device during placement and soldering of the device relative to a substrate surface such as a printed circuit board.